This invention relates to multi-channel generating systems and, more particularly, to a system having improved circuitry for detecting an underspeed condition.
Generators may be coupled in parallel to multi-channel operation to provide current to a load. For example, in a four-engine aircraft, four-channel operation is provided, each engine being a prime mover for one channel. When a prime mover for one channel is shut down, the rotor of the generator tends to motor the prime mover. This is undesirable and results from a voltage impressed on the stator of the shut-down channel by the other operating channels. An overrunning clutch has been coupled between the output of the constant speed drive and the rotor of the generator portion of a generator. For example, see Baits U.S. Pat. No. 3,576,143, which shows an integrated constant speed drive generator having an overrunning clutch which slips as the speed of the prime mover decreases below minimum speed. Simultaneously, the drive charge pressure between the constant speed drive section of the system and the rotor of the generator section decreases, until an underspeed pressure switch is actuated. The switch provides a signal to the generator control unit to remove the excitation voltage from the exciter of the generator and to open the line contactor, thereby electrically disconnecting that channel from the multi-channel system. The generator control unit receives power from a permanent magnet generator (PMG) mounted on the rotor of the generator.
It is desirable to eliminate the underspeed pressure switch from the constant speed drive for a number of reasons. The first is that since the underspeed switch is physically located near the prime mover and the generator control may be in a remote location, the elimination of the switche eliminates a significant amount of copper conductor. In a four-engine commercial aircraft, for example, approximately 1,000 feet of interconnecting wire is eliminated.
We have developed an improved integrated constant speed drive generator for use in a multi-channel generating system which does not require the use of an underspeed pressure switch, thereby minimizing the use of interconnecting wire within the system and reducing the number of parts in the system.